A foodstuff using soybeans as a raw material, such as soy milk, is rich in dietary fiber and has a high nutritional value, and hence is attracting attention from a viewpoint of health as well. A beverage is a general application method for soy milk. As an application method for soy milk other than the beverage, in Non Patent Document 1, there is proposed production of a fermented foodstuff obtained by fermenting soy milk into a yogurt form with existing lactic acid bacteria. In addition, in Patent Document 1, there is proposed a fermented foodstuff obtained by fermenting powdered soy milk using soybean flour as a raw material with lactic acid bacteria. However, in Non Patent Document 1, 8 hours or more of the fermentation is required in order to obtain the fermented foodstuff of a yogurt form, and in Patent Document 1, the fermentation is performed for 12 hours or more. That is, when soybeans are used as a raw material, a long fermentation time is needed in order to obtain the fermented foodstuff of a yogurt form. When a long fermentation time is needed as described above, there is a problem in that application to a commercial production line is difficult.
Further, a commercially available fermented soybean foodstuff does not curdle without a thickener, and hence needs the thickener. However, there is a problem in that incorporation of the thickener degrades qualities, such as taste, sourness, and smoothness.